Wash beetroot well and trim but leave the skins on. Place beetroots ,1 cup of vinegar and rapadura sugar in a medium saucepan. Pour water into the saucepan until beetroots are just covered. Bring to the boil and leave to simmer for 30 minutes or until tender. While the betroots are cooking, finely chop the fresh mint and roughly chop the silverbeet. When beetroots are cooked, peel or rub off skin and chop into small pieces. Add the mint and silverbeet to the hot diced beetroots and stir through so that they wilt slightly. Top salad with crumbled feta and drizzle with a little balsamic vinegar. Serve by itself or as a side.